1. Field of the Invention
The present invention relates to stable aqueous suspensions, of silica-aluminates known as zeolites, which suspensions also have good fluidity.
2. Description of the Background
The zeolites are increasingly used in detergent formulations as replacements for polyphosphates, which, when discharged into the environment, are responsible for eutrophication of lakes and rivers.
To facilitate the use of zeolites during the production of detergent formulations, zeolites are increasingly employed in the form of c. 50% aqueous suspensions of anhydrous zeolite. These suspensions must then be employable in industry; i.e. they must be pumpable after being transported from the production location to the utilization location, and/or after storage for several days prior to utilization.
Over a long time, various adjuvants have been proposed which enable production of stable suspensions of zeolites. Thus, Fr. Pat. 2,287,504 and Eur. Pat. 0,294,694 describe the preparation of suspensions of zeolites stabilized with surfactants belonging particularly to the family of fatty alcohols with 10-18 C atoms ethoxylated with 1-8 moles of ethylene oxide. This solution has the drawback of requiring the use of large quantities on the order 0.5-6%, on the basis of the total weight of the suspension, of the stabilizing agent.
Fr. Pat. 2,512,690, discloses the stabilizing agents which are hydroxylated polymers which are starch derivatives. These have been found to be efficacious, but must be used in large quantities, amounting to 0.4-2.5 wt. %, based on the total weight of the suspension.
Ger. Pat. 3,021,295 describes a stable composition of zeolites containing 15% of nitrilotriacetic acid in salt form. The discharge of wastes containing this product is strictly regulated at present, and in certain countries is prohibited.
Fr. Pats. 2,455,479 and 2,461,516 claim stabilizers in the form of polymers which have the drawback of causing the release of ammonia in the strongly alkaline medium (pH 10-13) of the zeolites in the case of Fr. 2,455,479, and in the case of Fr. 2,461,516, the drawback is lack of assurance of good stability during the preparation, storage, and shipping of the zeolite suspensions when temperatures are in the range 50.degree.-60.degree. C.
Fr. Pat. 2,658,095 describes the use of crosslinked acrylic copolymers as stabilizing agents. This solution also has the drawback of requiring excessive amounts of stabilizer the order of 0.4 wt. % on dry basis, based on the total weight of the suspension. A need continues to exist for aqueous zeolite suspensions of improved fluidity and stability characteristics.